Brushless motors have been known, in which coils of individual phases are concentrically wound about respective stator poles (e.g., see Patent Document 1). FIG. 130 is a schematic vertical cross section illustrating such a conventional brushless motor. FIG. 129 is a cross section taken along a line AA-AA of FIG. 130. These figures show a 4-pole 6-slot type brushless motor. The stator has a so-called concentrated winding structure in which the stator poles are concentrically imparted with turns of coils of the respective phases. FIG. 131 shows a state where the stator has been developed along the circumference by one cycle. The figure shows an arrangement of the windings U, V, W and the like. The horizontal axis indicates electrical angle in which one cycle corresponds to 720°. N- and S-pole permanent magnets are circumferentially and alternately arranged on a surface of a rotor 2. U-phase stator poles TBU1 and TBU2 of a stator 4 are imparted with turns of U-phase windings WBU1 and WBU2, respectively. Similarly, V-phase stator poles TBV1 and TBV2 are imparted with turns of V-phase windings WBV1 and WBV2, respectively. W-phase stator poles TBW1 and TBW2 are imparted with turns of W-phase windings WBW1 and WBW2, respectively. Brushless motors having such a structure are widely spread, currently, for industrial and household uses.
FIG. 128 is a transverse cross section illustrating a configuration of another stator. The stator shown in FIG. 128 has a 24-slot configuration which may enable distributed winding for 4-pole motors. This stator may allow its circumferential magnetomotive force distribution to have a comparatively smooth sinusoidal form. For this reason, this type of stator is widely used, for example, for brushless motors, field winding type synchronous motors and induction motors. In particular, rotating magnetic fields are desired to be accurately formed by a stator in case, for example, of synchronous reluctance motors and various types of motors applying reluctance torque, or induction motors. For these motors, a concentrated-winding stator structure shown in FIG. 112 is suitable.
Patent Document 1: Japanese Patent Laid-Open No. 6-261513 (See page 3 and FIGS. 1 to 3.)